# Block Pulled Up Slope/Coefficient Of Kinetic Friction.

1. Nov 2, 2008

### kaylanp01

1. The problem statement, all variables and given/known data
Block A has a mass of 5.56 kg and is on a rough incline of 21.5 degrees to the horizontal. Block B has a mass of 4.66 kg and the coefficient of kinetic friction between Block A and the plane is 0.276. What is the acceleration of the blocks?

2. Relevant equations
I used a = m2g - m1gsin(theta) / (m1+m2)
I see why thats wrong though, because I didn't use the kinetic friction.

3. The attempt at a solution
Again, I used the eq above to get
a = (4.66)(9.81) - (5.56)(9.81)sin(21.5) / (5.56+4.66) = 2.52 m/s^2

But I see why thats incorrect, I just don't know the correct method. haha.

Thanks! :)

2. Nov 2, 2008

### Staff: Mentor

I don't understand the setup. How are the two blocks related?

3. Nov 2, 2008

### kaylanp01

just a sec, i'll draw a picture.

Sorry that it took me a while to reply, I'm still working on the remaining questions.

4. Nov 2, 2008

### Staff: Mentor

Well then, add the kinetic friction. What's the formula for finding the friction force? What's the normal force?

5. Nov 2, 2008

### kaylanp01

I have N=f/mu but I don't know F or N. Hah. I'm usually not this terrible at physics, I promise.

6. Nov 2, 2008

### Staff: Mentor

To find the normal force, analyze forces on the block perpendicular to the incline surface.

7. Nov 2, 2008

### kaylanp01

See, thats the part that confuses me, the drawing of the arrows on the diagram. How do you know what direction N is pointing in? Whats mg? Etc.

I'm really not understanding this entire topic.